Radioactivity Flashcards
What is background radiation?
Radioactive sources found all around us
What are the sources of background radiation?
In the air( as radon gas)
From space(cosmic rays)
From devices such as X ray tubes
Nuclear weapons and power stations
What was the plum pudding model?
The plum pudding model( made by JJ Thomson) suggested that atoms were spheres of positive charge with tiny negative electrons stuck in them like a plum pudding.
Describe the experiment that Marsden and JJ conducted
They fired positive alpha particles at thin sheet of gold foil. They expected the positive alpha particles would be slightly deflected by the electrons in the ‘plum pudding’ model.
What were the results and conclusions?
Results:
Most alpha particles passed through the metal foil undeviated
Conclusions::
- Most of the mass of an atom is concentrated in the centre of a tiny nucleus
- Nucleus is positively charged, as it repels positive alpha particles
- Nucleus of much smaller then the atom br dude most alpha particles passed through undeviated. It also shows that most of the atom is empty space
Why can’t we tell when decay happens?
Because it is random
What is the new atomic model?
Nucleus is tiny but makes most of an atoms mass. Nucleus has an overall positive charge. The radius of the nucleus is about 10 000 times smaller than radius of atom. It contains positive protons and an equal amount of negative electrons orbiting around the shells of an atom. It contains neutrons, which are uncharged.
Most of the atom is empty space.
Why was Rutherford’s model quickly accepted?
It predicted the existence of a neutron
It explains radioactivity in terms of changes that happen to an unstable nucleus when it emits radiation.
It agreed with measurements Geiger and Marsden made in their experiments!
What are alpha particles?
alpha particles are helium nuclei emitted by some radioactive substances. These have a relative atomic mass of 4 and a charge of 2. They are relatively big and slow moving, so they do not penetrate far into materials and are stopped quickly- even in air.
Because of their size they are strongly ionising - meaning they bash into lots atoms and knock electrons from them before they slow down, which creates a lot of ions.
What are beta particles?
Beta particles are fast moving electrons. It is emitted when an unstable nucleus that contains too many neutrons decays. For every beta particle emitted, a neutron turns into a proton in the nucleus.
They are moderately ionising. These have virtually no mass and a charge of -1
What is gamma radiation?
Gamma radiation is electromagnetic radiation. It is just energy and does not change the element of the nucleus that emits it. It is weakly ionising due to its penetrating nature, so they tend to pass straight through, rather than collide with atoms. Eventually they hit something and do damage.
What is the nature of alpha,beta and gamma radiation through fields( electromagnetic and magnetic)?
These are used to separate them.
Alpha and beta deflected in opposite directions due to their opposite charge. Alpha feels a greater force( due to its larger charge) ,but is deflected less because it has a greater mass.
Game rays are not deflected as they have no mass or charge
What is ionisation?
Ionisation is when a radioactive substance knocks electrons out of around and atoms become charged because they lose electrons.
Dangerous because it can call call mutation, which results in cancer
How do we protect ourselves from radioactive sources?
Hold at arms length with tongs and use for short time.
Always store in lead boxes and use lead aprons!
What stops: alpha, beta and gamma?
Alpha is absorbed by paper and even skin. Short range in air.
Beta is absorbed by aluminium or any other metal.
Gamma is absorbed by less or a concrete.
